DOI 10.4110/in.2009.9.2.41 REVIEW ARTICLE PISSN 1598-2629

Regulation of Immune Responses by the Activating and Inhibitory Myeloid-Associate Immunoglobuline-Like Receptors (MAIR) (CD300)

Akira Shibuya*, Chigusa Nakahashi-Oda and Satoko Tahara-Hanaoka Department of Immunology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki 305-8575, Japan

Activating and inhibitory cell surface receptors play im- steps of the activation response. portant roles in regulation of immune responses. Recent In contrast, the activating receptors have a short cytoplas- progress has demonstrated that many inhibitory receptors mic domain and contain a charged amino acid residue in the pair with activating, as well as inhibitory, isoforms, both of transmembrane region, which is involved in association with whose are located in small clusters on a . immunoreceptor tyrosine-based activating motif (ITAM)-bear- We and others identified paired activating and inhibitory im- ing adaptor transmembrane , such as Fc RI or DAP12, munoglobulin-like receptors, designated myeloid-associated or with DAP10 adaptor containing PI3 binding motif immunoglobulin-like receptors (MAIR) (CD300). MAIR is a (5,6). These adapter proteins are tyrosine phosphorylated by multigene family consisting of nine genes on a small segment of mouse chromosome 11. MAIR family receptors are prefer- the src family tyrosine (PTKs) Syk or Zap70 entially expressed on myeloid cells, including macrophages, upon binding, resulting in activation of down stream dendritic cells, granulocytes, and bone-marrow-derived cul- signaling molecules in lymphoid and myeloid cells. Recent tured mast cells, and a subset of B cells and regulate activa- progress has demonstrated that many inhibitory receptors pair tion of these cells. Thus, MAIR plays an important role in in- with activating, as well as inhibitory, isoforms (2,7), both of nate immunity mediated by myeloid cells. whose genes are located in small clusters on a chromosome [Immune Network 2009;9(2):41-45] (8). Myeloid cells, including neutrophils and macrophages, play an essential role for host defenses against infectious microbial pathogens (9). Myeloid cells are activated through a vast ar- INTRODUCTION ray of cell surface receptors, such as Fc receptors for IgG, β2 integrins, complement receptors, chemokines, Activating and inhibitory cell surface receptors play important receptors and Toll-like receptors, and mediate , roles in regulation of immune responses (1,2). The immune degranulation of anti-microbial substances or secretion of in- inhibitory receptors contain immunoreceptor tyrosine-based flammatory mediators. However, how activation of myeloid inhibitory motif (ITIM) in their cytoplasmic domains. The pro- cells is regulated is incompletely understood. We and others totype 6-amino acid sequence for ITIM is (I/V/L/S)-x-Y-x-x- identified and characterized paired activating and inhibitory (L/V) (x denotes any amino acid), whose tyrosine is phos- immunoglobulin-like receptors, designated myeloid-associa- phorylated upon ligand binding, providing a docking site for ted immunoglobulin-like receptors (MAIR)-I and MAIR-II and the recruitment of Src homology 2 (SH2)-containing cytoplas- MAIR-IV and MAIR-V, whose extracellular domains are highly mic (3,4) and shutting down activation signals conserved with each other, respectively. In this review, we by dephosphorylation of intracellular substrates at the earliest describe molecular and functional characteristics of the MAIR.

Received on March 23, 2009. Accepted on March 31, 2009. *Corresponding Author. Tel: 81-29-853-3474; Fax: 81-29-853-3410; E-mail: [email protected]

Keywords: MAIR, CD300, activating , inhibitory receptor

IMMUNE NETWORK http://www.ksimm.or.kr Volume 9 Number 2 April 2009 41 Regulation of Immune Responses by MAIR (CD300) Akira Shibuya, et al.

IDENTIFICATION OF THE MAIR a short (20 aa) cytoplasmic tail (Fig. 1). The MAIR-I and MAIR-II genes are located to the proximal region of E2 band To identify novel genes encoding cell surface receptors in- of mouse chromosome 11. MAIR-I and MAIR-II are also volved in immune responses by myeloid cells, we performed named as CLM8/LMIR1 and CLM4/LMIR2/DIgR1, respectively representative differential analysis (RDA) which is a PCR- (10-12). based subtractive hybridization, using day 14 fetal livers from By screening a database for the mouse , we and PU.1-/-mice lacking myeloid cells and control littermates. others found that MAIR-I and MAIR-II are members of a multi- Among several cDNA clones unique to myeloid cells identi- family consisting of nine genes on a small segment of fied, we found a novel gene encoding a member of the Ig mouse chromosome 11 (11,13) (Fig. 2). superfamily, designated MAIR-I. The cytoplasmic domain of We cloned all the full-length cDNAs of the MAIR family MIAR-I contains the ITIM-like sequences (VEY258STL and genes other than MAIR-I and MAIR-II by PCR from the spleen LHY270SSV, respectively) based on the consensus sequence of C57BL/6 mice and designated them as MAIR-III to MAIR- for ITIMs (I/V/L/SxYxxL/V) (Fig. 1), suggesting that MAIR-I IX, based on a phylogenetic tree analysis (Fig. 3). We found may recruit protein tyrosine phosphatases and mediates in- that one of the genes, MAIR-IV, has a short cytoplasmic tail hibitory signals. We also identified a clone encoding the pro- (24 aa) with no signaling motif and a negatively charged glu- tein, designated MAIR-II, which contains one Ig-like domain tamic acid (E) in its transmembrane (TM) region (Fig. 1). The with 92% amino acid identity to that of MAIR-I in extracellular Ig-like domain of MAIR-IV in the extracellular portion has domain, a transmembrane region with a charged aa (Lys) and 91% identity with that of MAIR-V at the amino acid level. In

Figure 1. Molecular characteristics of MAIR. MAIR family receptors belong to immunoglobulin superfamily with one in the extracel- lular portion. MAIR-I and MAIR-II and MAIR-V and MAIR-IV are paired inhibi- tory and activating receptors, respective- ly, with high homology in the extracel- lular portion each other. MAIR-I and MAIR-V contain immunoreceptor tyrosi- ne-based inhibitory motif (ITIM) in their cytoplasmic domains and mediate inhi- bitory signals. MAIR-II and MAIR-IV as- sociates immunoreceptor tyrosine-based activating motif (ITAM)-bearing adaptor transmembrane proteins Fc RI or DAP12 and mediate activation signals.

Figure 2. Gene localization of MAIR family. Mouse and human MAIR family genes are mapped on chromosome 11 and 17, respectively.

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Figure 3. Molecular phylogenetic tree of MAIR gene family. Phylogenetic analysis of the MAIR family genes was performed by using the UPGMA method of GENETYX-MAC software (Software develoment, Tokyo, Japan). MAIR-II, MAIR-III, MAIR-VII and MAIR-VIII contained a charged amino acid in the transmembrane portion, and some of them associate with ITAM-bearing adaptor. MAIR-I and MAIR-V contains ITIM in the cytoplasmic portion. contrast to MAIR-IV, MAIR-V has a long cytoplasmic tail con- MAIR-I contains the ITIM sequences in the cytoplasmic do- taining two consensus immunoreceptor tyrosine-based in- main and inhibits IgE-mediated degranulation from mast cells hibitory motif (ITIM), suggesting that MAIR-IV and MAIR-V (19). Analyses by using the transfectant of rat basophil leuke- constitute paired activating and inhibitory receptors (Fig. 1). mia RBL-2H3 expressing wild type or variable mutant MAIR-I MAIR-IV and MAIR-V were also named as CLM5 and CLM1/ at Y233, Y258, Y270 and/or Y299 demonstrated that both Y258 and DIgR2 (11,14,15), respectively. The MAIR family was found Y270, but not Y233 and Y299, were phosphorylated and recruits to be a murine counterpart of the human CMRF-35 (CD300) SHP-1and SHIP upon cross-linking of MAIR-I, which were es- family (16-18), which is located on human , sentially required for inhibition of IgE-mediated degranulation syntenic region of mouse chromosome 11 (Fig. 2). from the RBL-2H3 transfectant (21). MAIR-II associates with the immunoreceptor tyrosine-based EXPRESSION AND FUNCTION OF MAIR-I AND activation motif-bearing adaptor DAP12 and stimulates pro-in- MAIR-II, PAIRED INHIBITORY AND ACTIVATING flammatory and chemokine secretions from peri- RECEPTORS, RESPECTIVELY toneal macrophages (19). However, we found that cross-link- ing MAIR-II with monoclonal induced secretion of MAIR-I is expressed on the majority of myeloid cells, includ- significant amount of the inflammatory cytokines TNF-α and ing macrophages, dendritic cells, granulocytes, and bone-mar- IL-6 from DAP12-/- as well as wild type peritoneal macro- row-derived cultured mast cells, and a subset of B cells, but phages. Further studies demonstrated that MAIR-II associates neither on T nor NK cells (19). In contrast, MAIR-II protein with not only DAP12 but also FcRγ chain homodimers in per- is detected only on cell surface of subsets of B cells and peri- itoneal macrophages (20). These findings present the first toneal macrophages (19,20). case of an activating receptor that uses either DAP12 or FcRγ

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chain as a signaling adapter. CONCLUDING REMARKS

EXPRESSION AND FUNCTION OF MAIR-IV AND MAIR family receptors are preferentially expressed on mye- MAIR-V, PAIRED ACTIVATING AND INHIBITORY loid cells, including macrophages, dendritic cells, gran- RECEPTORS, RESPECTIVELY ulocytes, mast cells, and a subset of B cells and regulate acti- vation of these cells. It is not clear at present how these acti- MAIR-IV was preferentially expressed on Gr-1high/Mac-1＋ vating and inhibitory receptors cooperate each other for regu- neutrophils from the peripheral blood, bone marrow, peri- lation of immune responses by myeloid cells. To understand toneal cavity and spleen. MAIR-IV was also expressed on the role of MAIR family receptors in immune responses, it Mac-1＋/Gr-1－ macrophages from the spleen and bone mar- is essentially required to identify their ligands and character- row and CD11c＋ dendritic cells (DC), but not on T, B, NK ize the receptor-ligand interaction in vivo. cells or bone marrow-derived cultured mast cells (13). MAIR-IV contains a short cytoplasmic tail with no signaling ACKNOWLEDGEMENTS motif, suggesting that MAIR-IV, like MAIR-II, mediates activat- ing signals via ITAM-containing adapter proteins, such as FcR- This research was supported in part by grants provided by γ chain or DAP12. DAP12 associates with several activating the Ministry of Education, Science and Culture of Japan and NK receptors and myeloid cell-specific receptors, including the Program for Promotion of Fundamental Studies in Health human and mouse TREM-1, TREM-2, MDL-1, and PILRβ, SIRP Science of the National Institute of Biomedical Innovation β1, mouse TREM-3 and CD200R3, CD200R4 and mouse (NIBIO). The authors have no conflicting financial interests. MAIR-II, all of which contain a positively charged amino acid, such as lysine (K) or arginine (R), in their TM region (22). CONFLICTS OF INTEREST In contrast, FcRγ chain is also able to associate with re- ceptors, such as FcγRIIIA and FcεRI, which do not contain The authors have no financial conflict of interest. a positively charged amino acid in the TM region (23). Because MAIR-IV does not possess a positively charged ami- REFERENCES no acid in the TM region, FcRγ chain might be a partner of MAIR-IV. In fact, MAIR-IV associate with FcRγ chain in 1. Ravetch JV, Lanier LL: Immune inhibitory receptors. peritoneal macrophages as well as transfectants expressing Science 290;84-89, 2000 MAIR-IV (13,14). Because MAIR-IV associates with FcRγ 2. Lanier LL: Face off--the interplay between activating and in- hibitory immune receptors. Curr Opin Immunol 13;326-331, chain, it may mediates an activating signal in neutrophils. 2001 Stimulation of MAIR-IV with plate-coated F(ab')2 fragments of 3. Malbec O, Fong DC, Turner M, Tybulewicz VL, Cambier anti-MAIR-IV mAb induced TNF-α and IL-6 secretion from JC, Fridman WH, Daëron M: Fc epsilon receptor I-asso- neutrophils or peritoneal exudatative cells, indicating that ciated lyn-dependent phosphorylation of Fc gamma re- ceptor IIB during negative regulation of mast cell acti- MAIR-IV is a novel activating receptor on neutrophils. vation. J Immunol 160;1647-1658, 1998 MAIR-V (CD300LF) was expressed on macrophages, but 4. Smith KM, Wu J, Bakker AB, Phillips JH, Lanier LL: Ly-49D not on B cells, T cells or granulocytes, derived from the sple- and Ly-49H associate with mouse DAP12 and form activat- en and peritoneal cavity (24). Cross-linking MAIR-V with anti- ing receptors. J Immunol 161;7-10, 1998 5. Lanier LL, Bakker AB: The ITAM-bearing transmembrane MAIR-V monoclonal antibody induced cell death in peritoneal adaptor DAP12 in lymphoid and myeloid cell function. macrophages as well as in several transfectants expressing Immunol Today 21;611-614, 2000 MAIR-V. 6. Love PE, Shores EW: ITAM multiplicity and thymocyte se- lection: how low can you go? Immunity 12;591-597, 2000 Scanning electron microscopy revealed loss of blebs from 7. Takai T, Ono M: Activating and inhibitory nature of the the surface of the dead cells mediated by MAIR-V, a morpho- murine paired immunoglobulin-like receptor family. Immu- logical feature similar to that observed in apoptotic cells. nol Rev 181;215-222, 2001 However, further studies revealed that MAIR-V mediates cas- 8. Martin AM, Kulski JK, Witt C, Pontarotti P, Christiansen FT: Leukocyte Ig-like receptor complex (LRC) in mice and pase and ER stress-independent cell death by a novel men. Trends Immunol 23;81-88, 2002 mechanism. 9. Nathan C: Neutrophils and immunity: challenges and op-

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